The correct response is:
It causes mixing of oxygenated (blood with oxygen in it) and deoxygenated blood (blood without oxygen in it), making it harder for the body to get the oxygen it needs.
In frogs, the heart consists of one ventricle, which leads to the mixing of oxygenated and deoxygenated blood. This mixing can reduce the efficiency of oxygen delivery to the body compared to a system with separate ventricles, like that of humans.